This invention relates to hydronic heating systems for dwellings, offices, etc. and more particularly to apparatus having supply header water temperature control and responding to outdoor ambient temperature for maintaining the system supply header water temperature within a predetermined range depending on the outdoor ambient temperature.
Hydronic heating systems for heating the rooms in a dwelling, office, etc, are used widely in Europe and to a lesser extent in the United States. Water heated in a boiler is distributed to heating loops of tubing in the dwelling that carry the heat by radiation, conduction and convection to the rooms in the dwelling. A common technique provides a boiler hot water supply feeding the supply header of the heating loops and the boiler water return to which the return header of the heating loops connects. The return water is heated in the boiler and sent out again as hot supply water, and so the water is cycled through the essentially closed system. One or more water pumps in this system keep the water flowing and valves control water flow rates through the loops depending on demand.
A heating loop may include several heating elements like wall mounted radiators and/or baseboard finned tubing that are the principal heat exchangers of the loop, or the tubing itself may be the principal heat exchanger of the loop. In the latter case the tubing is usually buried in the floor of a room and the tubing heats the floor. Often the tubing is buried in a special concrete and so heat exchange is principally by conduction and radiation to the concrete, which in turn heats the room by some conduction and convection, but principally by radiation. Hence, this type of heating is called Radiant Floor Heating (RFH).
In such RFH systems and other hydronic heating systems using wall radiators and/or baseboard finned tubing elements, the supply water temperature from the boiler must be controlled so that it does not exceed certain limits that are substantially lower than the usual boiler supply water temperature. There are several reasons for this: first, the temperature of radiator elements on the wall must not be so high that they are not safe to touch; second, for RFH the floor temperature must not be uncomfortable hot; and third, where the tubing is plastic, the water temperature for some plastic materials must not exceed about 140.degree. F. Good quality "cross-linked" polyethylene tubing, on the other hand, can carry water at temperature in excess of 140.degree. F. without any deterioration of the tubing or the tubing oxygen barrier.
In hydronic heating systems subject to such water temperature limitations, where the boiler is powered by burning fossil fuels, the boiler water supply temperature is usually well above 140.degree. F. and often at about 180.degree. F. to 200.degree. F., and so the boiler supply temperature must be stepped down before it is fed to the heating loops. In the past, an electrically controlled motorized mixing valve has been used in the boiler supply line that feeds the supply header for the heating loops, between the boiler supply and the heating loops supply header. This mixing valve has two inputs and one output. One input is directly from the boiler hot water supply, the other input is from the return header of the heating loops and the output is directly to the supply header of the heating loops. The mixing valve motor is electrically energized by remote reset controls that sometimes respond to outside ambient temperature, inside room temperature, boiler water temperature, supply header water temperature, etc. In operation, the mixing valve mixes some return water with the hot supply water to reduce the temperature of the supply water that is fed to the supply header of the heating loops. Such prior systems perform quite satisfactorily, but they are relatively expensive, require remote transducers and electric power to the valve's motor and relatively greater skill to install and adjust for efficient operation.
In an effort to reduce expense, non-motorized mixing valves have been used in the boiler supply line. These have the disadvantage of providing less comfort and lower long term fuel economy. However, for the small installation (kitchen-bath addition, etc. to a dwelling), where it is difficult to justify the cost of a more sophisticated motorized valve and its electric controls, these systems are sometimes used. They usually have a remote electrically operated room thermostat controlling a circulator wired through a surface aquastat to prevent overheated water from entering the heating loops; and on the boiler supply line is a dial thermometer that indicates the supply water temperature into the loop supply header. However, manually setting the water temperature into the heating loops by adjusting the valve setting is not precise. Often within a few hours after start up, when temperatures throughout the system have stabilized, fluctuations of the boiler supply water temperature, or varying load conditions at other parts of the system will cause excessive fluctuations of water temperature delivered by the valve to the heating loops supply header. These systems have no feedback control to the mixing valve that is derived from the heating loop supply header water temperature.
Use of non-motorized valves with supply header water temperature feedback is a substantial improvement and is described in my U.S. Pat. No. 5,119,988, which issued Jun. 9, 1992, entitled: Hydronic Heating Water Temperature Control System. That patent describes several hydronic heating systems with a non-motorized (non-electric) valve having supply water temperature feedback to the valve controller. In some of those systems, the valve is a return valve in the return water line and in another system, it is a mixing valve in the supply water line. The diverting valve and the mixing valve are quite different. The diverting valve has one input and two outputs and diverts water from the return line (on the way from the heating loop return header to the boiler return), to the boiler supply line that feeds the loop supply header, diluting the supply water (reducing its temperature) that is fed to the heating loop supply header. The mixing valve has two inputs and one output and mixes some of the cooler return water with the hot supply water from the boiler and feeds the mixture (diluted supply water) to the heating loop supply header.
That patent teaches use of a non-electric thermostatic actuator head attached to the valve for positioning the valve stem and controlled by a capillary temperature sensor. Thus, the valve is modulated by non-electric feedback of the diluted supply water temperature. As described in that patent, the bulb of the capillary sensor is inserted into the diluted supply water or it may be clamped to the supply line next to the supply header so that it is at the temperature of water in the supply header. Capillary fluid in the bulb expands with temperature applying a pressure force through the capillary to the actuator head and so the valve is modulated to increase or decrease the flow of return water through the valve as necessary to maintain the temperature of the heating loop supply header water at or below a predetermined value. That value can be set by a mechanical setting on the actuator head. This set point control configuration insures that an accurate reading of the supply header water temperature is made continuously and simultaneously any deviation from the setting is immediately hulled by modulating the valve.
The several embodiments of the present invention are improvements to such hydronic heating systems having a non-motorized, non-electric, feedback controlled valve for controlling heater loop supply header water temperature, depending on outdoor ambient temperature.